1. Field of the Invention
The present invention relates to a communication system, and more particularly to a method and system for transmitting/receiving data which can minimize InterCarrier Interference (ICI) in a communication system using a multicarrier.
2. Description of the Related Art
In communications, the most essential issue is to efficiently and reliably transmit data over a channel. The next generation multimedia mobile communication system, which is currently being developed, requires a high-speed communication system capable of processing and transmitting various information, such as image and radio data, beyond the early voice-oriented service. Therefore, it is necessary to increase system efficiency by using a channel coding scheme appropriate for the system.
Unlike a wired channel environment, in a radio channel environment of a wireless communication system, errors inevitably occur because of various factors, such as multipath interference, shadowing, propagation attenuation, time-varying noise, interference, and fading, resulting in a loss of information. The loss of information causes serious distortion of the transmission signals, thereby degrading the entire performance of the communication system. To reduce the loss of information, various error control techniques are used to increase the reliability of the system according to channel characteristics in which a basic technique is to use an error-correcting code.
In the next generation communication systems, research is actively being conducted to provide users with high-speed services having various Qualities of Services (QoS). As a next-generation communication system, a system (hereinafter, referred to as an OFDM/OFDMA communication system) employing an Orthogonal Frequency Division Multiplexing (OFDM) scheme and an Orthogonal Frequency Division Multiple Access (OFDMA) scheme has been proposed.
In order to remove ICI occurring in the OFDM/OFDMA communication system, various schemes, e.g. a scheme using frequency or time domain equalization, an ICI removal scheme using a code rate, and a frequency-domain partial response encoding scheme, have been proposed. The scheme using frequency or time domain equalization is the most general scheme which removes ICI by using a Minimum Mean Square Error (MMSE), Zero-Forcing (ZF), and a Decision Feedback Equalizer (DFE), in which a receiver estimates ICI and then performs an equalization operation based on the estimated ICI. Therefore, the scheme using frequency or time domain equalization has an advantage in that it is possible to efficiently remove ICI when the degree of change in a channel is small, but has a disadvantage in that the construction of a receiver for equalization can be complicated when the degree of change in a channel is large.
The ICI removal scheme using a code rate, e.g. the ICI removal scheme using a code rate of 1/k (k≧2), is performed in such a manner that one data symbol is multiplied by pre-defined weighting coefficients and is mapped to one group of subcarriers in the frequency domain, or that windowing is performed in the time domain by using only one subcarrier among one group of subcarriers. Therefore, according to the ICI removal scheme using a code rate, a receiver can identify a reception signal in which ICI has been cancelled through signal processing. Also, according to the ICI removal scheme using a code rate, a receiver can cancel more ICI in such a manner as to combine a plurality of subcarrier reception signals contained in one group in the frequency domain by means of the same weighting coefficients as a transmitter, or to use only one reception signal among subcarrier reception signals contained in one group after performing windowing in the time domain. The ICI removal scheme using a code rate has advantages in that it can easily and efficiently reduce ICI, and that a receiver has a more simple construction than that for the scheme using frequency or time domain equalization, but has a disadvantage in that a spectral efficiency corresponding to a code rate is reduced by 1/k times.
In addition, according to the frequency-domain partial response encoding scheme, Partial Response Coding (PRC) used for suppressing intersymbol interference in a single subcarrier system is performed in order to remove the ICI of transmission signals input to an Inverse Fast Fourier Transform (IFFT) module of a receiver. Therefore, according to the frequency-domain partial response encoding scheme, a carrier-to-interference ratio (CIR) after encoding becomes greater than that before encoding, so that ICI is efficiently removed. Although the frequency-domain partial response encoding scheme does not reduce the efficiency in the frequency band, the frequency-domain partial response encoding scheme has problems in that the effect is small in removing ICI, and that the construction of a receiver for signal detection is complicated because the receiver employs a Maximum-Likelihood Sequence Estimator (MLSE).
Therefore, it is necessary to develop a method for solving the above problems, that is, a data transmission/reception method for reducing the complexity of a receiver, improving the performance of the system, and minimizing ICI.